Lithium ion batteries having a high energy density and high voltage are commercially available and widely used. The electrode used in a lithium ion battery is a key factor influencing the performance of the cell. Anode electrodes usually have an intrinsic first cycle irreversible capacity loss due to the formation of a solid electrolyte interphase (SEI) along with other irreversible reactions between lithium and the anode. This first cycle irreversible capacity loss consumes valuable lithium from the more expensive cathode materials. The degree of first cycle irreversible capacity loss varies depending on the nature of the active materials, other components in the battery, and the preparation of the anode. This value ranges from 10 to 30 percent for anodes based on carbon materials, and can be substantially higher for anodes based on other types of active materials, such as tin, selenium, and silicon. As such, the first cycle irreversible capacity loss substantially increases the cost of lithium ion battery fabrication and yields a larger dead weight within the lithium ion battery.
To further enhance the energy density of secondary lithium batteries, a wide range of non-lithiated cathode materials, such as sulfur, V6O13, V2O5, MnO2, and FeSe2, have been investigated. High capacity cells have been demonstrated when using non-lithiated cathode materials with lithium metal as the anode. However, direct use of lithium metal as an anode is not safe due to dendrite formation that causes shorts in the cell. Therefore, several approaches have been developed in order to enable non-lithiated high capacity cathode materials. These approaches generally fall into two categories: (1) prelithiation of the anode in order to remove the first cycle irreversible capacity loss; or (2) modification of the lithium metal to improve its cycle performance and safety when incorporated with an anode.
Prelithiation of the anode is performed via the following two approaches: (i) adding n-butyllithium (or another lithium-containing chemical) onto an anode laminate and subsequently washing the laminate with a hydrocarbon solvent such as hexane to remove any unreacted chemicals and unwanted products; or (ii) attaching a lithium foil onto the surface of anode laminate and subsequently adding an electrolyte to initiate the lithiation reaction. After a certain period of time, the residual lithium foil is removed. Through controlling the lithiation time and/or weight of lithium foil, one can obtain electrodes with different degrees of lithiation. The prelithiated anode electrodes made by these approaches may then be used for battery assembly. While these two approaches illustrate that an anode can be prelithiated, they are difficult to scale up for industrial battery fabrication.
Stabilized lithium metal powder (SLMP), a lithium powder coated with either a thin layer of a lithium salt or wax as a protection layer, has also been investigated as the lithium source for the lithiation of anode electrodes. The lithium salt coated SLMPs have been found to be incompatible with N-methylpyrrolidinone (NMP), dimethylformamide (DMF), and dimethyl acetamide (DMA) in attempting to generate slurries of electroactive materials—in fact, attempting to generate a slurry of lithium salt coated SLMPs and NMP results in a highly dangerous exothermic reaction. Unfortunately, NMP, DMF, and DMA are the three commonly used solvents for the most widely used binder in lithium ion cells, polyvinylidene fluoride (PVDF). To circumvent this, a surface spray coating approach was developed where SLMPs with either a lithium salt layer or a wax layer are spray coated onto the surface of a pre-made anode laminate, followed by carlendering the laminate to break the surface coating layer of the SLMP. The anode is then prelithiated in situ upon addition of an electrolyte. However, this surface spray coating approach is difficult to scale up because the surface spraying technique suffers from clogging issues.